The Parasitic Diseases Research (PDR) Program of Puerto Rico unites three investigators at UPR Rio Piedras on a common interest, schistosomiasis. This parasitic disease, which the WHO TDR Program has designated as one of the major parasitic diseases of mankind is endemic in Puerto Rico, the only area under the U.S. flag in which this statement can be made. PI Hillyer seeks to characterize and isolate schistosome-specific worm and egg antigens important for the immunodiagnosis of infection, develop monoclonal antibodies to them, and develop sensitive and immunologically specific optimal high throughput serodiagnostic systems (RIA, ELISA) utilizing state of the art technology: Pl File seeks to examine the interaction of Schistosoma eggs with the cells of the intestinal connective tissue to determine how the egg migrates through the tissues, an important and fundamental biologic question. This will be accomplished primarily utilizing scanning electron microscopy. Pl Hazen seeks to focus on determining the lethal dose for pathogenic bacteria in mice that are already infected with Schistosoma mansoni, S. Japonicum or both. He will also examine the ability of different common bacterial pathogens which are found in human feces to fatally (LD50) infect mice during different stages of the schistosome infection. Although each Pl has a proposal which stands alone, each proposal has interactive components with another investigator.